Heretofore, piping materials made of a metal such as lead-plated steel pipes, copper pipes and lead pipes have been used as a piping material for cold and hot water supply. However, there are problems, for example, when steel pipes are used the water color changes to red or black due to rust. In the case of copper pipes pinholes and blue piping, materials free from such problems are sought. Thus, piping materials are been used of which the materials comprise of a synthetic resin such as poly(vinyl chloride), polyethylene or poly(1-butene). These piping materials are not usually affected by the formation of rust or pinholes due to electrolytic corrosion.
Among these piping materials made of a synthetic resin, piping materials comprising a poly(1-butene) resin are excellent in pressure tight strength, high temperature creep resistance, heat resistance, and flexibility. Therefore, poly(1-butene) resins are one of the most suitable materials useful as a piping material for cold and hot water supply. Thus, it is expected that the demand for pipes comprising this poly(1-butene) resin will increase.
Although available poly(1-butene) resins are excellent in rididity, creep resistance, impact resistance, crystallization speed and the like, they have a narrow molecular weight distribution such that the ratio (Mw/Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) is 6 or less. Therefore, when such a resin is molded into a pipe having an aperture of 30 mm or less, it can sufficiently be molded at a low molding speed (3 m/min or less), but when it is molded into a pipe at a higher molding speed, rough surfaces arise on the inner or outer surfaces of the resulting pipe. These rough surfaces give the pipe a poor appearance. Therefore, a problem exists in molding poly(1-butene) resin at high molding speeds.